This invention relates to apparatus and method for generating a plasma employed to thin film deposition, etching and the like.
Recently, a plasma treatment is widely used in semiconductor manufacturing processes Which require micro-fabrication. In general, a cylindrical plasma etching apparatus, parallel plate plasma etching apparatus, microwave plasma etching apparatus and the like is well known as those for plasma treatment. A magnetron etching system is also developed for generating a magneto-exited plasma from a treatment gas by magnetron discharge with an RF electric field and a magnetic field. In the magnetron etching system, an efficiency of plasma generation is made high by applying the magnetic field to the plasma.
An example of conventional plasma treatment apparatus and method is described with reference to the drawings.
FIG. 17 is a sectional front view of the conventional plasma treatment apparatus, and FIG. 18 is a sectional plan view thereof. In the figures, a reference numeral 1 indicates a treatment chamber. 2 is a cathode. 3 is an anode. 4 is an article-to-be-treated. 5 is a power source. 6 is a gas inlet. 7 is a pumping port. 8 is a magnetic field applying device.
As shown in FIG. 17, the article-to-be-treated 4 is placed on the cathode 2 Which is connected to the power source 5. The anode 3 is grounded. A treatment gas is introduced to the treatment chamber 1 from the gas inlet 6. The treatment gas is, for example, 50 sccm CHF.sub.3. The pressure in the treatment chamber 1 is controlled to a desired pressure of, for example, 5 Pa by pumping through the pumping port 7. Thereafter, an RF electric power of, for example, 13.56 MHz and 800 W is applied to a space between the cathode 2 and the anode 3 from the power source 5 to generate a plasma. A direction of an electric field 9 between the cathode 2 and the anode 3 is indicated by arrows in FIG. 17.
As shown in FIG. 18, a magnetic field 10 whose magnetic lines of flux are uniformly in parallel with one another at least on the article-to-be-treated 4 is applied by the magnetic field applying device 8 to the space between the cathode 2 and the anode 3 concurrently with the application of the electric field. The electric field 9 in FIG. 17 (not shown in FIG. 18) is applied at a right angle to the paper of FIG. 18.
In the presence of the electric field 9 and the magnetic field 10 which intersect with each other, Lorentz force acts on each of charged particles in the plasma. Therefore, the charged particles drift in a direction of arrows D in FIG. 18, while gyrating in a cycloid motion. This drift increases the number of collision of the charged particles, increasing a degree of ionization of the gas, and thus creating a plasma. The article-to-be-treated 4 is exposed to the plasma to carry out the plasma treatment such as etching.
With the above conventional construction in FIGS. 17 and 18, however, the magnetic field 10 is applied in parallel on the article-to-be-treated 4, which causes nonuniformity of plasma density due to drift of charged particles. In detail, the charged particles move in the direction indicated by the arrows D in FIG. 18 (upward in the paper). Therefore, electrified regions which are polarized to a positive region and a negative region are generated at both ends of the article-to-treated 4 (upper and lower parts of the paper). Such charge-up damages the article-to-be-treated 4 owing to static electricity. For example, in a process of manufacturing a semiconductor device, this means breakdown or degradation of the semiconductor device. At a manufacturing process of highly integrated semiconductor device, the yield is lowered.
To solve the above problem, a method for contemplating a uniformed plasma density by rotating a magnet is employed. FIG. 19 is a sectional front view of a conventional magnetron etching system having a rotary magnet. The magnetron etching system 30 is essentially composed of a sealed treatment chamber 21, a pair of upper and lower electrodes 22, 23 opposed to each other with a space left between them in the treatment chamber 21, a magnet 29, as a magnetic field applying device, rotatably arranged outside of the treatment chamber 21 and above the upper electrode 22, and an RF power source 32 for supplying an RF electric power to a space between upper and lower electrodes 22, 23.
An object, e.g., a semiconductor wafer A (hereinafter referred to it as wafer) which is a substrate to be treated is etched in the treatment chamber 21. Inside of the treatment chamber 21 is kept vacuum by pumping means (vacuum pump) 25 connected to a pumping port 31 provided at a lower side part of the treatment chamber 21. A bottom wall composed of the lower electrode 23 and a side wall of the treatment chamber 21 are insulated from each other by an insulating member 34. The lower electrode 23 has at its center a disk-shaped susceptor 24 and the wafer A is supported on the susceptor 24. For supporting the wafer A on the susceptor firmly, a chuck mechanism such as an electrostatic chuck 26 is provided on the susceptor 24 to attract and hold the wafer A.
A disk-shaped space 27 is formed inside of the upper electrode 22 so as to oppose to the susceptor 24, and a plurality of gas diffusing pores 28 communicate with the space 27 so as to let the treatment gas through into the treatment chamber 21. A treatment gas supplying source 37 is connected via a massflow controller 36 to a gas introducing pipe 35 which is connected with a gas supplying passage 39 communicating with the space 27, so that the treatment gas (100 sccm CHF.sub.3, for example) supplied from the treatment gas supplying source 37 is introduced into the treatment chamber 21 via the space 27 and the diffusing pores 28. Heating means for heating the treatment gas over an air temperature as needed may be provided to supply the treatment gas through the heating means.
A temperature adjusting mechanism (not shown) capable of setting the temperature of the wafer A to a desired temperature (-100.degree. C. to +200.degree. C., for example) is provided at the lower electrode 23. The RF power source 32 whose one end is grounded is connected via a capacitor 33 to the lower electrode 23. The RF power source 32 supplies an RF electric power of, for example, 13.56 MHz to the space between upper and lower electrodes 22, 23. Thus, an electric field is applied to the wafer A.
The magnet 29 provided outside of the treatment chamber 21 and above the upper electrode 22 forms a magnetic field in a direction in parallel with a surface of the wafer A. The magnet 29 is rotated at a desired speed by a driving mechanism (not shown) such as a motor to form the magnetic field in a direction intersecting with the electric field applied to the wafer A.
For etching the wafer A by a system with the above construction, the wafer A is conveyed from a spare room (not shown) into the treatment chamber 21 via a load-lock chamber, and is positioned and attracted on the electrostatic chuck 26. Thereafter, the vacuum pump 25 pumps up the air in the treatment chamber 21 from the pumping port 31 to be 5 Pa.
Then, the treatment gas is supplied from the space 27 via the diffusing pores 28. When the RF power source 32 supplies the electric power to the space between upper and lower electrodes 22, 23, the electric field is generated at a right angle to the surface of the wafer A. Concurrently, since the magnetic field is applied by the magnet 29 to the space between upper and lower electrodes 22, 23, the magnetic field 38 in parallel with the surface of the wafer A and the electric field intersecting with the magnetic field 38 are formed and a magneto-excited plasma is generated by magnetron discharge. With the plasma the wafer A is etched.
According to the conventional magnetron etching system with the rotary magnet, the local nonuniformity of plasma density is averaged with its passage of time, but momentary plasma densities are still not uniform.
FIG. 20 is a schematic plan view showing a relation between the wafer A as a substrate to be treated and the magnetic field 38 at a moment in the magnetron etching system in FIG. 19. FIG. 21 shows distributions of a plasma density, an etch rate E/R and an electric potential V.sub.DC at a section (X--X section on a P-Q plane) intersecting at right angle with the magnetic field 38 in FIG. 20. Since the charged particles drift in a direction of an arrow D in FIG. 20 owing to Lorentz force, the plasma density and the etch rate on the P-Q plane of the wafer A are decreased from P toward Q and the potential V.sub.DC is increased inversely. Accordingly, the plasma density and the potential V.sub.DC are nonuniform, so that the electrified regions polarized to a negative region and a positive region are caused at both ends of the wafer A. Such charge-up may cause dielectric breakdown of a gate oxide layer of the wafer A and degradation of property thereof. It may be considered that ion sheath has a gradient in the surface of the wafer A because of a gradient of the potential V.sub.DC therein, therefore etching formation shall be deflected because ion travels in a direction intersecting at a right angle with the sheath.
A method that a plasma density is decreased to a degree not to damage a wafer is proposed as another etching method. However, the etch rate and throughput are lowered.